tevent: Only call handlers that ask for events

tevent: Only call handlers that ask for events

The s3 libsmbclient puts two different handlers on a single fd for readability
and writability. With select this works fine, however without this patch we
unconditionally call the write handler even if the socket is only readable. We
should have called the read handler instead.

Autobuild-User: Jeremy Allison <jra@samba.org>
Autobuild-Date: Wed Oct  6 23:40:24 UTC 2010 on sn-devel-104